Twenty years of CWACing the Bot River Estuary

The 25th of July1993 marked the first Coordinated Waterbird Count (CWAC) for the Bot River Estuary, one of the largest estuarine systems in the Western Cape. It was one of the first wetland sites to be counted soon after the CWAC programme was launched in 1992. The 6th of July 2013 will mark the 20th anniversary of these counts which have been coordinated by Mariana Delport of the Tygerberg Bird Club. Counts and observers have undergone various changes through the years. Says Mariana, "The first count was originally scheduled for 17 July 1993, but due to bad weather conditions it was postponed to 25 July 1993. Initially we only counted the Bot River Estuary (known locally as the Botriviervlei), but from 1995 we included the nearby Kleinmond Estuary as the two systems are closely linked."

The CWAC pioneers, made up of four teams, included Mariana Delport, Willie D’Hondt, Colin Jones, Jurie and Adele Fourie, Anton Nel, Mossie Smit, John and Debbie Philogene, Margaret McCall, Talitha le Seur, Brian Vanderwalt, Ann Rickets, Libby Kerr, Brenda Anderson and Beverley Patterson. From this group Mariana and Beverly remain as active counters! Additional counters from Kleinmond, Hermanus, Somerset West and Cape Town have given of their time to assist with the counts over the last 20 years.

Most counts have taken place twice a year (February and July), but from January 2003 until December 2006, all sections were counted to monitor the changes within a full breaching cycle of the estuary. The results were included as a chapter in Doug Harebottle's PhD thesis and which had important conservation outcomes for the estuary's waterbirds. Quarterly counts were then done for another three years. Mariana comments, "This called for some dedication, especially for us driving all the way from Cape Town, sometimes in adverse weather conditions!"

This is an incredible data set and probably one of the longest running series of waterbird counts for a South African estuary. Mariana says, "Looking at the results of the past 20 years, not much has changed since 1993. Numbers of Red-knobbed Coot, Yellow-billed Duck, Cape Shoveler, Red-billed Teal, grebes, flamingos, terns, shorebirds, have varied seasonally as well as based on the breaching regime of the sand bar at Meerensee". But she adds, "...some species, such as Red-knobbed Coot and Great Crested Grebe have seen gradual declines in numbers and in more recent years we have seen an increase in the number of Blue Crane along the upper reaches of the lagoon, which is great. Occasionally some rarities make their appearance, like Osprey, Black Harrier, Common Black-headed Gull and African Openbill."

The ADU salutes Mariana, her team and the Tygerberg Bird Club for taking ownership of this important wetland as a CWAC site over the past twenty years. It takes dedication and commitment to sustain monitoring at these levels. Like Stan Madden and the Blesbokspruit wetlands, Mariana has been the stalwart and champion for the Bot estuary CWACs.

We are also extremely grateful to all the citizen scientists who have given up their time, petrol and effort to help with these counts. Ensuring continuity for these counts is vital to understand the long-term dynamics of waterbird populations and everyone's contributions makes a difference; in Mariana's words "Let’s continue for another 20 years!"

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